High Performance Polyamides Fulfill Demanding Requirements for Automotive Thermal Management Components
Because they maintain excellent strength and toughness during exposure to hot, aggressive automotive fluids and to hot air whether humid or dry, high performance polyamides (HPPA) can make durable, functional components for automotive thermal management and other demanding applications.
The use of engineering thermoplastics in automotive components has grown significantly over the last 25 years with many new applications in powertrain, electrical components, chassis, trim components and other vehicle areas. Typical modern vehicles have more than 100 kg of plastic components. Some of the main forces driving demand growth include weight reduction, production gains (easier assembling, integration of parts and systems) and more design flexibility.
Under-the-hood applications have shown particularly high growth. Typical examples include air intake manifolds, rocker covers, radiator end tanks, fuel rails, electrical connectors and others. Polyamides have had great success in those areas due to their excellent balance of oil resistance, thermal stability, mechanical strength, toughness and other desirable properties.
In recent years, temperatures in the engine compartment have been rising because of reduced space and more powerful engines. The temperature resistance of plastics parts has consequently become even more critical. Weight reduction also continues being an issue to help reduce fuel consumption. These factors can be expected to lead to increased use of polymers with higher temperature performance such as PPAs.
The resistance of PPA’s to antifreeze is another factor in their favor. In an investigation of the effect of antifreeze solutions on polyamides in 1995, Garrett and Owens concluded that the performance of semi-aromatic PPA is superior to that of aliphatic polyamides such as nylon 6 or nylon 66. We have extended their study by measuring the performance of different types of PPAs and their resistance to today’s more aggressive long-life coolants in 5000 hour tests consistent with today’s extended warranty intervals.
BACKGROUND ON POLYMER CHEMISTRY
Polymers consist of repeating units of monomers (individual molecules) that combine to form a long chain. The polymers may consist of a single type of molecule (known as a homopolymer) or may be combinations of more than one molecule (known as a copolymer).
A major class of polymers known as thermoplastics may be remelted, as opposed to thermosets, which form irreversible crosslinks between polymer chains. Within the thermoplastics category, there are amorphous and crystalline polymers. Amorphous polymers have random orientation of their polymer chains, whereas crystalline polymers form highly ordered crystal structures within an amorphous matrix The term semi-crystalline polymers are used for polymers containing both crystalline and amorphous regions.
As a general rule, amorphous polymers have advantages of transparency and toughness. Semicrystalline polymers have advantages in chemical resistance and temperature performance. These are general statements however, and the designer must consult product-specific literature and test data for specific properties.
The polymers being discussed include aliphatic polyamides such as nylon 6 or 66, which are in the middle temperature range of semi-crystalline thermoplastics, and PPA, which is in the upper temperature range of the semicrystalline thermoplastics.
Polymers are often used in combination with other ingredients to make a useful product. This combination of polymer and additives is often referred to as a plastic, or a composite. Typical ingredients used to produce composites are fiberglass, mineral, heat stabilizers, flame retardants and other processing aids. Most of the products we discuss in this paper are composites with 30 to 35% by weight of fiberglass reinforcement, or GR for short (Glass Reinforced). Fiberglass reinforcement provides strength and stiffness particularly as the temperature is increased beyond the polymer’s glass transition temperature (Tg), where the amorphous region becomes mobile.